1. Field of the Invention
The present invention relates to a method and apparatus for adjusting a color of a moving image or a still image, and more particularly, to a method and apparatus for selectively converting a specific color of an image to another color.
2. Description of the Related Art
A method for color conversion or color adjustment of an image includes dividing an image signal into hue, brightness, chroma, and saturation signals and one-dimensionally processing the signals. The method has been disclosed in U.S. Pat. No. 5,202,935, U.S. Pat. No. 5,515,172, U.S. Pat. No. 5,930,009, U.S. Pat. No. 6,122,012, and U.S. Pat. No. 6,476,793. The method is inexpensive since a color conversion process is relatively simple. However, in this method, the degree of freedom of selecting a color region is reduced. Typically, an H-S plane is represented in polar coordinates where H is indicated by an angle and S is indicated by a distance from an origin, and a region on a color space selected by one-dimensionally combining these two coordinates becomes a sector. However, it is difficult to select a color indicating a specific object, for example, a blue sky color, a skin color, or a green grass color, because this color is correlated with a memory color, and the memory color is represented in general as an ellipse, not a sector in the H-S plane.
Referring to U.S. Pat. No. 5,202,935, discontinuity of a color space is generated as a conversion result, a converted image may become unnatural since an entire space has not been used, and color discontinuity may be generated between adjacent pixels in an image space. Referring to U.S. Pat. No. 5,930,009, color conversion can be selectively controlled for each of the R, G and B channels. However, color adjustment cannot be performed for each specific region on a color space or an image space. Referring to U.S. Pat. No. 6,122,012, since the number of controllable colors is limited to 6, other colors cannot be converted. Referring to U.S. Pat. No. 5,515,172 and U.S. Pat. No. 6,476,793, after matching an original hue value to a target hue value, a chroma value and a brightness value are properly converted. Since the original hue is matched to the target hue, colors in a specific region centering around the original hue are moved to colors in a specific region centering around the target hue. A result of the movement causes discontinuity of a color space. Accordingly, a converted image becomes unnatural.
Another method for color conversion or color adjustment of an image includes selectively performing color adjustment for each of the image components. The method has been disclosed in U.S. Pat. No. 6,262,812. In this method, division of the image components, e.g., division of a bitmap, a text and a graphic, must be performed in advance. Even if division of the image components has been performed, selective color adjustment for a specific color included in the bitmap cannot be performed.
Another method for color conversion or color adjustment of an image includes selectively performing color adjustment for each of the conversion regions. The method has been disclosed in U.S. Pat. No. 5,876,286. According to this method, a 2-D color space is divided into combinations of small triangles, and each triangle is set to a basic unit of a conversion region. In this method, by sending all colors of a region of the non-converted triangle to a region of the converted triangle, conversion from a triangle to another triangle is performed. Therefore, when the conversion is completed, the color space region of the non-converted triangle is empty. Accordingly, since discontinuity of a color space is generated, a converted image becomes unnatural.